Backside-Illuminated Photoelectrochemical (Bipec) Etching

Brief Description

A novel etching process that utilizes photo-generated holes to permit the electrochemical etching of a material, such as a III-Nitride, under conditions with which it would otherwise not etch.

Background

It is often desirable in semiconductor processing to have an etch that provides control over both the geometry and morphology of the material to be shaped. Variation of factors, such as concentration and temperature, can be used to tune purely chemical etches in order to produce crystallographic, or isotropic, etches. Although the use of a current or a voltage has been a long-established method of controlling etching, the absorption of light by a semiconductor has only recently been investigated as a further means to control etching. This method, known as photoelectrochemical (PEC) etching, has demonstrated several benefits over other etchings. For example, precise control over the requisite above-bandgap illumination allows for the rapid and inexpensive production of straight, low-damage sidewalls. While this method may be useful for mesa-or via-etching, it is highly undesirable for undercut etching. As a result, undercut etching has been done by purely chemical or electrochemical means. In the III-Nitrides, undercut etching has not been possible since neither of these means are available for this class of materials.

Description

Scientists at the University of California have developed a novel etching process that utilizes photo-generated holes to permit the electrochemical etching of a material, such as a III-Nitride, under conditions with which it would otherwise not etch. Depending upon the conditions and materials used, this method may produce a variety of etch morphologies, such as inverted cones and undercut structures.

Advantages

•  Enables the etching of otherwise inert chemistries, such as the etching of III-Nitride in KOH;

• Achieves large lateral etch rates suitable for removal of overgrown material, such as GaN, from the substrate, or the formation of structures exhibiting large undercuts.

Applications

This invention has applications in semiconductor wafer processing, particularly in a photoelectrochemical etching geometry that can produce strong undercuts and new morphologies. Some useful morphologies involving the III-Nitrides include:

• Fabricating inverted cones or spikes;

• Etching undercuts;

• Etching deep undercuts, using either bandgap or dopant selectivity to enhance the depth;

• Lift-off layers from their as-grown substrates.

Patent Status